1. Field of the Invention
The present invention relates generally to semiconductor processing. More particularly, the present invention relates to a method for determining the endpoint of a process performed within a processing chamber.
2. Background of the Related Art
In the field of integrated circuit and flat panel display fabrication, multiple deposition and etching processes are performed in sequence on the substrate within one or more processing chambers to form various design structures. Processes such as physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, etc. are well known in the industry and each result in residue build up in the chamber. For example, during CVD, silicon oxide or silicon nitride materials are deposited on all exposed surfaces in the CVD deposition chamber, as well as on the substrate. Such residues, which may accumulate to a thickness of as much as 0.5 to 10 microns, usually must be removed from the chamber surfaces prior to the next deposition process. Otherwise, the material may flake off and deposit on a substrate, thereby compromising the integrity of features formed thereon.
Conventionally, chambers are cleaned to remove the residue using a plasma and select chemical compounds which react with the residue and form a volatile compound which can be exhausted from the chamber. Alternatively or additionally, the chemical compounds may form etching species which bombard the chamber surfaces to dislodge residue from the chamber components.
When the chamber cleaning operation is performed, the production of semiconductor devices can not continue. As a result, the effective productivity of the chamber, as measured by substrate throughput, decreases significantly. In order to increase the chamber productivity, it is necessary to quickly finish the cleaning operation and restart the production promptly after the end of the cleaning operation. Therefore, it is imperative to precisely determine the endpoint of the cleaning process.
One method of detecting the end point of the cleaning process monitors a variation in a prescribed light wavelength emitted by the plasma. However, it is difficult to correctly detect the end point of the cleaning operation using this method because light emitted from lamps used to heat the substrate also heats, reacts with or otherwise affects the wavelength monitor, distorting the wavelength reading and resulting in over-cleaning or under-cleaning.
Another method of detecting the endpoint of a cleaning process was to observe the conditions within the chamber through a quartz view port. During processing within the chamber, residue accumulates on the view port, thereby blocking the view into the chamber. As the cleaning process is performed, the material is removed from the view port and all the other surfaces in the chamber as well, until the view port is cleaned and line of sight into the chamber is restored. Once line of sight into the chamber has been restored, the process is continued for approximately 20 to 30 seconds to ensure that the cleaning process is complete. The line of sight detection method does not provide an accurate determination of the endpoint and requires additional insurance cleaning time to assure adequate cleaning of the chamber.
In the area of integrated circuit fabrication, time spent in processing and cleaning is an important issue which manufacturers monitor. Time spent cleaning the chamber can be a limiting factor in the capabilities of their production. Accordingly, there is a need for an accurate and consistent determination of the endpoint of a process performed in a chamber. Preferably, the determination can be made using existing hardware and monitors.